Systems exist for varying the valve timing in a four-stroke internal combustion engine. One such system, used in some Honda engines, is the Variable Valve Timing and Lift Electronic Control (VTEC) system. This is an electronic and mechanical system that allows the engine to have multiple camshafts. VTEC engines have an extra intake cam having its own rocker which follows the cam. The profile on this cam keeps the intake valve open longer than the valves in non-VTEC engines. At low engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves.
Another system for varying valve timing involves advancing the valve timing. By advancing the valve timing, the valves are opened later and closed later. This is accomplished by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins. The valve, for example, might open at 10 degrees after TDC and close at 210 degrees after TDC. Closing the valve 20 degrees later is not optimal, and it would better to be able to increase the duration that the intake valve is open.
Several problems exist, however, for the systems described above. The Honda VTEC system, for example, harbors two disadvantages—the complexity of an additional cam shaft, with added rocker arms and piston/actuator assemblies, and the step function valve timing change (i.e., off/on) from one valve timing mode to the other. The complexity of the additional cam shaft confers additional production costs (additional components to be produced and assembled), and reduced reliability (additional components to wear/fail). Furthermore, this design is not amenable to retrofitting in existing engine/head designs because retrofitting would require a completely new head design for the engine to be retrofitted due to the VTEC's additional cam shaft assembly.
The problems associated with the step function valve timing change of the VTEC system include only one valve timing mode being available based upon the engine's speed (i.e., rotations per minute (RPMs)). At low speeds, one mode is available, while at some other speed the alternate timing mode is automatically selected. Therefore, only two engine speeds will afford optimum engine efficiency. All other engine speeds will suffer some degradation of efficiency. Thus, there is a need for an infinitely variable valve timing system which optimizes efficiency throughout the engine's RPM range and overcomes the problems associated with existing variable valve timing systems.